Cluster: A small local area network (LAN) with fewer than 32 nodes
Modular System: A spatially concentrated cluster conforming to the present invention (e.g. a cluster concentrated within a single box/housing), wherein the data transmission medium of the respective LAN is a bus having characteristic,short length and ultra high speed of operation, and wherein computers at the network nodes of the cluster have modular form; facilitating their use as either workstations or network servers or both workstations and servers.
Presently, when plural computers are used within the confines of a single residence or commercial plant or office, it is common practice to link such computers into a LAN by externally attaching the computers to media used in such networks. Typically, this is done to enable the computers and their user(s) to share access to stored data and to data communication networks external to the respective LAN (e.g. the Internet, the telephone system, etc.). In this environment, connection of the LAN to external networks is usually provided through a hub, switch and server that control routing of data both between the LAN and the external network as well as between individual computers in the LAN.
A disadvantage of this is that handling of local transfers through the hub effectively increases traffic loads at the hub, switch and server, so that the volume of peak traffic that can be moved through these elements is less than it could be if local transfers were not being handled through the hub.
The present invention seeks to provide a more efficient arrangement for handling local data transfers within such networks.
In accordance with the present invention, a modular system is provided as defined above, containing a concentrated LAN composed of computers connected by an ultra high speed bus which serves as both a network transmission medium, between computers at nodes of the respective LAN, and a conventional parallel-transfer bus medium for connecting individual computers in the system to shared storage resources which are accessible to those computers only through the bus.
Used as a network transmission medium, the bus enables any computer in the system to transfer data packets to any or all other computers in the respective modular system. Such packets are encapsulated in a header, unique to the respective LAN, designating the origin and destination(s) of the data, and can be of arbitrary length. Thus the amount of data in a transmitted packet can be significantly greater than the amount of data which can be transferred over the bus in a single cycle of conventional parallel-transfer operation.
As presently contemplated, a concentrated LAN in accordance with our invention is actually a virtual construct used by the computers in the respective modular system; i.e. it is a construct used by emulation software applications executed by these computers. Within this construct each computer in the system has a uniquely defined network address or pseudo-port (also termed xe2x80x9cvirtualxe2x80x9d port) which has no significance external to the respective system. Thus, use of these pseudo-ports effectively isolates computers at nodes of the respective concentrated LAN from external networks, and also serves to maintain compatibility between operations of LAN emulation applications and operating system software such as Windows NT used at these nodes. More specifically, in respect to software compatibility, the pseudo-port construct allows for modular transmissions on the bus of the respective modular system to contain control signals which need not correspond to control signals used for conventional paralleltransfer operations on the same bus. These and other advantages of the isolation and compatibility features associated with use of the presently contemplated pseudo-port construct will be readily appreciated by those knowledgeable in the arts associated with contemporary data networks and computer systems.
The modular forms of the computers in the subject concentrated LAN allows for a computer at any node to be configured for operation as either a workstation or a network server between a network external to the respective concentrated LAN and other nodes of that LAN, or even as both a workstation and external network server. Furthermore, the transmission protocol used in the subject LAN is compatible with protocols used in external networks so that routing of data packets between an external network and a node of the concentrated LAN requires only a simple modification of header intelligence accompanying the packet.
In a preferred embodiment of the invention, the modular system contains a host computer, plural client computers, the high-speed bus and storage resources that are managed by the host computer subsystem through a connection thereto separate from the high-speed bus and access to which is shared by the client computers via the highspeed bus. A feature of this arrangement is that it allows for the host computer subsystem to efficiently manage the shared storage resources and initial diagnostics of the systems, while the LAN emulation protocol presently contemplated allows any client computer to efficiently transfer network data packets directly to any or all other computers (both client and host) in the respective modular system without requiring intermediate routing of such packets through the host subsystem or any other component of the system that could be likened to a hub of a more conventional LAN.
Another feature of this invention is that when a modular system transfers data packets from a network external to the system to an internal node on the system""s bus, the system computer interfacing between the external network and the modular system bus employs plural levels of network emulation. At a first such level, the interfacing computer encapsulates a data packet in a first level header, that header indicating origin and destination addresses unique to the respective concentrated LAN and having no extrinsic meaning or context in the external network, and in a second level emulation, the interfacing computer encapsulates the transferred packet in an additional second level header indicating origin of the packet in the external network. In a transfer in the reverse direction, from concentrated LAN to external network, a similar two-level emulation is used to indicate internal origin and destination addresses in the concentrated LAN and a destination address in the external network. It is understood of course, that a packet originating and terminating within the module system is encapsulated only in the first level header.
In an outgoing transfer to the external network, the first level header effectively designates the port on the system bus which connects to the computer system that interfaces to the external network as an interim xe2x80x9cinternalxe2x80x9d transfer point for the packet, and the second level header indicates the origin and final destination of the packet in global terms that are unique to and meaningful in the external network.
Thus, client computers in the modular system can exchange data as peers, using only the first level LAN emulation, and such exchanges have no impact on the volume of data traffic between the concentrated LAN and external networks. Furthermore, computers in the concentrated LAN cluster can route data to and receive data from an external network, using the first and second levels of LAN emulation, without burdening any computer that is not directly involved in such transfers. These functions distinguish the present system from conventional LAN clusters wherein data flowing between internal nodes of the cluster are required to be routed through hubs carrying data between the local cluster and external networks, and thereby add to the traffic burdens of such hubs.
Using the first and second levels of LAN emulation, packets passing between the internal bus of a concentrated LAN and an external network undergoes format conversions at the pseudo-port interfacing to that network. Thus, packets on the bus are invariably in a form in which destinations inside the local cluster are unambiguously distinguishable locally from external destinations, and packets being routed to or from a terminus outside the cluster are always in a form in which origins and/or destinations outside the cluster are globally recognizable in the external network.
This type of arrangement is particularly effective in computer clusters conforming to the modular architectures described in the above-referenced co-pending patent application by Heath et al entitled MODULAR ARCHITECTURE FOR SMALL COMPUTER NETWORKS. In such systems, computer modules forming the locally concentrated LAN or cluster consist of a host computer, storage resources, and bus residing on a system board, and client computers that plug interchangeably into sockets on the system board which connect to the bus. This type of system is tightly concentrated into a small space or box comparable in size to the space occupied by the housing of a contemporary personal computer system. The system bus that necessarily has a small length due to this concentration of the elements that it connects, can be operated at data transfer rates much greater than transmission media used in traditional local area networks (LAN""s), having longer lengths (e.g. lengths measured in feet or kilometers, as compared to the inches of the present system bus) so that transfers of the additional digits required to provide the foregoing first and second levels of encapsulation have negligible impact on the traffic handling capacity of the bus.
According to another aspect of the invention, computers constituting components of a presently contemplated modular system as defined above employ a network emulation protocol configuring the computers in the system into a virtual LAN, which protocol enables each computer in the system to direct transfer of a packet of data to any other computer in the system, via the system""s bus, and also enables each computer in the system to direct a packet transfer concurrently to a plurality of other computers in the system via that bus.
A feature of the just-mentioned network emulation protocol is that it also enables each computer in the modular system to initiate a failure indication to the other computers via said virtual LAN, without being requested to do so, and it also allows each computer to remove itself from and re-insert itself into the virtual LAN without having to be commanded to do so by another computer in the system.
The foregoing and other features, benefits and advantages of the present invention will be more fully understood by considering the following description and claims.